1-1/2 miles
north of West Chesterfield. All of these localities lie in an area
mapped as Conway schist by Emerson. The Conway schist is described as
dark graphitic mica schist, containing biotite, garnet, staurolite, and
zoisite, and beds of impure limestone and quartzite. In each case
pegmatite is the matrix for the tourmaline and other minerals found.
At
the Barrus prospect a pegmatite ledge has been traced by outcrop and
surface bowlders for a distance of over 200 yards. Starting from the
south side of the spring the ledge outcrops in a N. 15° W. direction
along the hillside, continuing through a small glacial valley at the
north end. The thickness of the pegmatite is not plainly exposed but is
probably as much as 8 feet in places. The wall rock is
garnet-staurolite schist of the typical Conway schist, striking
parallel with the pegmatite and dipping east. The pegmatite is only
medium coarse to fine grained. No crystal-lined cavities or pockets
were observed. The quartz of the pegmatite occurs in small masses
thickly scattered through the rock. The feldspar is chiefly albito,
some of the rough crystals measuring nearly 6 inches thick. In places
the albite has a slightly tabular development, forming small crystals
like clevelandite. The mica is mostly greenish muscovite, but a little
pale pink lepidolite was observed associated with clevelandite. Gray
to pale yellowish-green translucent spodumene is abundant in crystals
ranging up to 2 inches long. One translucent aquamarine-colored beryl
crystal was found in the pegmatite in close association with the
spodumene. Indigo-blue to bluish-black tourmaline crystals are
scattered through much of the pegmatite. These crystals range from
minute size up to half an inch thick and several inches long. Most of
them have dark-blue to black cores with lighter blue shells. A few
crystals with bluish-green shells were observed. All of the tourmalines
found are opaque to translucent and no transparent ones were seen. No
pink or red crystals were observed, but Gibbs states that they occur,
but are rare.
Most
of the work done here consists of blasting and breaking of surface
bowlders and outcrop. Much of the ledge is concealed by deep humus and
leaf mold soil which makes careful prospecting difficult. Before
thorough prospecting can be carried on, much of the surface would have
to be stripped of the soil covering.
Clark's
ledge is a large prominent outcrop of pegmatite, outcropping along an
east sloping hillside in a N. 10° W. direction for about 150 yards. The
lower side forms a small cliff 30 feet high in places. The pegmatite is
inclosed nearly conformably with the garnet-staurolite schist wall rock
cutting across the schist with offsets to the southeast at intervals.
It is split by a horse of schist into two ledges 6 to 10 feet thick at
the north end, and has a thickness of 15 feet toward the south end.
Some of the feldspar of this ledge is in rough crystals. Quartz occurs
in small irregular masses, some of which have a peculiar translucency.
Beryl crystals are rather plentiful, some showing translucent
aquamarine colors. Emerson marks this ledge as carrying spodumene, but
none was observed in the brief examination made. Mica occurs in
yellowish-green plates up to 3 inches in diameter. Opaque red garnets
and a little biotite occur in the pegmatite. Only black and
bluish-black tourmaline crystals were observed, but evidently the vein
described by Gibbs was not found. Gibbs mentions a "false" vein, 6
inches to 1J feet thick, cutting obliquely across the ledge for a
distance of about 20 feet.
